Biopsy systems for breast computed tomography

ABSTRACT

A device and methods for performing a simulated CT biopsy on a region of interest on a patient. The device comprises a gantry ( 22 ) configured to mount an x-ray emitter ( 24 ) and CT detector ( 26 ) on opposing sides of the gantry, a motor ( 28 ) rotatably coupled to the gantry such that the gantry rotates horizontally about the region of interest, and a high resolution x-ray detector ( 172 ) positioned adjacent the CT detector in between the CT detector and the x-ray emitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/717,886, filed Dec. 17, 2019, which is a continuation of U.S.application Ser. No. 15/669,829, filed Aug. 4, 2017, now U.S. Pat. No.10,548,549, which is a divisional of U.S. application Ser. No.11/913,494, filed Nov. 2, 2007, now U.S. Pat. No. 10,492,749, which is aU.S. National Stage Entry under § 371 of International ApplicationPCT/US2006/017146, filed May 3, 2006, which is based on U.S. ProvisionalApplication 62/677,704, filed May 3, 2005, each of which is herebyincorporated by reference.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant Nos.EB002138 and EB89260, awarded by the National Institute of Health. Thegovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention pertains generally to imaging of a patient's breast, andmore particularly to improved methods and apparatus for breastdiagnosis, evaluation and therapy through CT imaging.

2. Description of Related Art

X-ray mammography is used as the primary breast cancer screening testworldwide, and recent reports have suggested that mammography has beenresponsible for a sizeable reduction in breast cancer mortality. Instandard mammography, the breast is generally compressed between tworadiolucent plates of a compression fixture, and an x-ray image is takenthrough the plates and breast. The compression flattens the breast todecrease obscuring overlap of breast structure.

When suspicious lesions are found in mammography, a biopsy may beperformed in which a needle is inserted into the breast tissue to obtaina sample of the tissue in the area of the lesion. In this case, thecompression fixture can be used to stabilize the breast between the timeof the image and the biopsy, guiding the biopsy needle in a manner thatensures its registration with the mammographic image.

Despite the important role that mammography plays in breast cancerscreening, it is well recognized that mammography has limitations,particularly in women with dense breasts. The sensitivity of mammographyaveraged over the population is estimated to be approximately 75% to85%, and models suggest that the sensitivity in dense breast is markedlylower. Further, even with compression of the breast, minor overlap ofnormal breast anatomy can sometimes obscure suspicious areas—especiallyin women with breast implants or very dense breasts. The compression canbe uncomfortable and may deter some women from regular mammograms.

X-ray computed tomography (CT) allows the internal structure of tissueto be clearly imaged without the need to flatten or otherwise distortthe tissue as is done in mammography. Nevertheless, standard whole-bodyCT is impractical for imaging the breasts because the axial scan used insuch machines would deposit significant radiation in the torso and lungsnear the breast. For this reason, specially designed CT machines havebeen proposed for imaging the breast (“breast CT machine”) in which thescan is conducted in the coronal plane rather than axially. In such asystem, the patient is positioned prone on a table. The table hasopenings in its surface admitting one or both breasts. A horizontallyopposed detector and x-ray source rotate below the table about avertical axis through the pendant breast. The smaller geometry of thismachine can further provide improved image resolution.

One important benefit of a breast CT machine is that the breast need notbe highly compressed as it is in conventional mammography. The reductionof compression needed to reduce the overlap of breast structure providesa more comfortable experience for the patient and can improve theimaging of some breast structure, such as breast ducts, which are undulydistorted by compression. One drawback to such breast CT machines, ininstances where a suspicious lesion is found and a biopsy is required,is that compression of the breast in a standard mammography fixture andpossibly re-imaging of the breast may be required to provide thenecessary guidance for the biopsy procedure.

SUMMARY OF THE INVENTION

The present invention provides a set of tools that improves the abilityto perform biopsies when using a breast CT machine. The invention allowsthe spatial coordinates of the suspicious lesions to be extracteddirectly from the breast CT images and these spatial coordinates to beused to guide a biopsy without repositioning or re-registration of thepatient.

The invention first provides a multi-image display of breast CT data inany of several different formats: axial slices, coronal, sagittal andaxial projections, volume rendered and/or virtual or actual compressionmammograms. Each image may have a cursor that tracks with cursors inother images following a common position within the breast. The cursorsallow accurate determination of the coordinates of the suspicious lesionas identified by a variety of methods including computer analysis ofimage/volume data and operator inspection of the images. As part of thisprocess, an iterative matching system makes it possible to superimposematching cursors, not only on the CT generated images, but on a standardmammogram taken earlier with a standard mammography machine.

Once the location of the suspicious lesion is identified, a roboticbiopsy system incorporated into the CT system may provide a biopsywithout the need to re-position the patient. Geometric correction of theCT machine using a specially designed phantom and/or the ability toimage portions of the robot, before and during the insertion of thebiopsy needle (using periodic updates of the breast image), allows anaccurate biopsy on the same machine. The breast may be stabilized duringthis process with a support, for example, a suction collar havingapertures for admitting a biopsy needle.

Alternatively, the present invention contemplates the possibility of avirtual biopsy on the same machine using a special high resolution CTdetector that may focus in on the lesion to provide more detailed data.The small area of the detector provides rapid acquisition of data whilelimiting radiation exposure. Image artifacts normally produced when CTreconstruction is applied to truncated projection data that does notfully span the breast are avoided by using the earlier lower resolutiondata used to locate the lesion to supplement the high-resolution data.

The present invention also contemplates several novel measurements ofthe breast, including measurements and characterization of ductalarchitecture of the breast and measurements and characterization ofbreast density, the latter based on proportions of glandular tissue tonon-glandular tissue. These measurements may provide for additionaldiagnostic information for the identification, detection, and treatmentof breast cancer and long-term monitoring of longitudinal changes breastcancer.

More specifically, in one aspect of the invention, a simulated mammogramis created from CT data by employing an algorithm for compressing thevolume data of the breast and projecting it into a two-dimensionalimage. A further aspect of the invention is employment of an algorithmto register the simulated mammogram to the patient's mammogram foridentification of anatomic structures and suspicious areas. Iteratingthe compression algorithm with small changes in individual compressionparameters (orientation, warping, scaling, shifting, elasticity, etc.)and comparing results, makes it is possible to (register) align thevolume breast CT data to pre-existing mammography views. Further thealgorithm may be employed to identify optimized views of suspiciousareas for the improving compression mammogram projection images.

The aligned breast image data can then be displayed side-by-side,permitting the mammographer to compare both sets of images.Additionally, once the compression parameters are known, it is possibleto co-locate lesions, suspicious findings, or other structures in oneset of images and have the compression algorithm depict the location inthe other images and volume data.

In a further aspect of the invention, CT volume data is used toaccurately guide needle-core biopsy using computer-controlled robotictechnology. Using this approach, the woman's breast is scanned using thebreast CT scanner. The radiologist or other physician then localizes thesite of suspicion in the volume data set using various image displaytechniques. From this data, computer algorithms guide the movement of amotion-enabled robotic arm for the placement of the needle biopsy gun ora guide into the optimal position so that the biopsy “gun” is accuratelypositioned for biopsy. The physician then activates the spring-loadedbiopsy gun to inject the needle to the site of the suspicious lesion.Alternatively, the computer can drive the needle to the suspected lesionunder image-guided control. The CT scanner and targeting algorithm canbe employed to provide periodic updates of the breast image data torefine the trajectory or path of the biopsy device optimizing accuratesampling of the target lesion.

In another aspect of the invention, a method of computing aphysiological characteristic of a target tissue in a patient's breastidentifies glandular tissue and provides a breast density measurementbased on relative proportion of glandular tissue in the breast. Thebreast density value may provide an indication of risk of breast cancer.

Yet another aspect of the invention may provide a simulated CT biopsy ofa region of interest on a patient using a separate high-resolution x-raydetector augmenting the standard detector and the x-ray emitter. Aplurality of actuators may be coupled to the gantry to move thecollimators and high-resolution detector in a sinusoidal pattern whilethe gantry rotates to keep it focused on a possible lesion to provide ahigh-resolution image of the lesion.

A further aspect of the invention is an apparatus for performing abiopsy on a region of interest of the patient. The apparatus comprises agantry configured to mount an x-ray emitter and a CT detector onopposing sides of the gantry, a motor rotatably coupled to the gantrysuch that the gantry rotates horizontally about the region of interestto generate CT images of the region of interest, and a robotic armconfigured to house a biopsy needle, wherein the robotic arm is furtherconfigured to position the needle at the location of interest based onthe CT images of the region of interest.

A further aspect is a device for immobilizing breast tissue bystabilizing a smaller region of interest on the breast. A method is alsodisclosed whereby the tissue is stabilized with a vacuum device thatfirmly holds the tissue without compression. An advantage of the currentmethod is that it operates only over a defined region, the size of whichcan be modified by using different applicators. The method furtheremploys vacuum stabilization such that tissue is most firmly stabilizedat the areas of contact of the applicator and the lines of force are inopposition to force lines for any interventional device appliance,minimizing tissue displacement during procedures. As a result, themethod provides optimal force management while minimizing tissue stress.The depth of the stabilization can be increased through use of largerapplicators. Larger tissue regions may also be stabilized withaugmentation via external compression plates or additional applicators.

Another aspect of the invention is an apparatus for generating the imageof a region of interest of a patient. The apparatus has a gantryconfigured to mount an x-ray emitter and a CT detector on opposing sidesof the gantry, a motor rotatably coupled to the gantry such that thegantry rotates horizontally about the region of interest to generate CTimages of the region of interest, and a PET detector coupled to thegantry to generate PET images of the region of interest substantiallysimultaneous with the CT images.

Another aspect of the invention is an apparatus for generating the imageof a region of interest of a patient. The apparatus has a gantryconfigured to mount an x-ray emitter and a CT detector on opposing sidesof the gantry, a motor rotatably coupled to the gantry such that thegantry rotates horizontally about the region of interest to generate CTimages of the region of interest, and an ultrasound scanner coupled tothe gantry to generate ultrasound images of the region of interestsubstantially simultaneous with the CT images.

A further aspect of the invention is a method for generating theprojection image of a region of interest of a patient. The methodincludes the steps of injecting a contrast agent into the region ofinterest, emitting x-rays through the region of interest, and acquiringprojection image data sets from a detector configured to detect theemitted x-rays passing through the region of interest.

A further aspect of the invention is a method for using a contrastmaterial and generating the CT images from the breast or a region ofinterest within the patient. The method includes the steps of injectinga contrast agent that arrives at the region of interest, emitting x-raysthrough the region of interest, and acquiring CT image data sets from adetector configured to detect the emitted x-rays passing through theregion of interest. Subsequently, CT images of the region of interestare produced demonstrating the lesion.

In one embodiment of the current invention, acquiring projection imagedata sets includes the steps of acquiring data from a low energyemission, acquiring data from a high energy emission, and obtaining adual energy subtraction image from the acquired data. The dual energysubtraction can be used with the injection of contrast agent to enhanceits appearance.

A further aspect of the invention is a method of calibrating a CTscanner by placing one or more objects having known dimensions andmaterial properties in the field of view of the scanner, tracking thelocation of the one or more objects with a tracking algorithm, and usingthe paths of the one or more objects to calibrate the CT scanner.

In yet another aspect of the present invention, a graphic user interface(GUI) for displaying CT images is disclosed. The GUI comprisessimultaneous display of two or more views of the CT image, wherein thetwo or more views depict planar or rendered views at different angularorientations from one another such that rotation of the image in thefirst view results in a corresponding rotation of the image in the otherviews. The GUI may also include alignment lines connecting a region ofinterest in the CT image in the first view to the corresponding locationof the region of interest in the second view. The GUI provides a cursorto designate locations of interest. Coordinates are then generated thatare used by an algorithm to provide a trajectory for the biopsy deviseand optimize that trajectory. In some situations updated image (CT, US,etc.) image information will be used to monitor and refine thetrajectory.

Yet a further aspect of the invention is a method of determiningabnormal structures in a patient's breast. The method includes the stepsof generating CT images of a series of reference patients, identifyingnormal duct structures in the generated CT images to generate a databaseof normal duct structures, generating CT images of a patient to bediagnosed, and comparing the CT images of the patient to be diagnosedwith the database to identify an abnormal structure in the patient'sbreast.

Further aspects of the invention will be brought out in the followingportions of the specification, wherein the detailed description is forthe purpose of fully disclosing preferred embodiments of the inventionwithout placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is side view of a horizontal CT breast scanner of the presentinvention.

FIG. 2A is a perspective view of a patient with breast positioned in thescanner of FIG. 1.

FIG. 2B is a side view of a patient with breast positioned in thescanner of the present invention.

FIG. 3 is a series of CT images taken at various coronal sections alonga patient's breast.

FIG. 4 is a schematic view illustrating an apparatus for simulatingmammogram compression of breast tissue using uncompressed CT volumedatasets.

FIG. 5 is preferred method of the present invention using a mathematicalcompression algorithm to transform the three-dimensional volume data setgenerated from a breast CT scanner.

FIG. 6 is a view of a display provided to a user of the CT allowingmultiple image representations linked by a common cursor.

FIG. 7 is a detailed flow diagram of the compression algorithm of thepresent invention.

FIG. 8 is a series of coronal CT views of a patient's breast.

FIG. 9 is an expanded view of one of the coronal views of FIG. 8.

FIG. 10 is a flowchart illustrating a method for computing breastdensity in accordance with the present invention.

FIG. 11 is a view of a histogram of the image shown in FIG. 10.

FIG. 12 illustrates breast density as a function of the patient's age.

FIG. 13 illustrates a perspective view of the operation of the CTscanner of FIG. 1.

FIG. 14 is a side view of the CT scanner shown in FIG. 13.

FIG. 15 is a top view of the CT image biopsy system of the presentinvention

FIG. 16 is a view of the CT image biopsy system of FIG. 15 after partialrotation.

FIG. 17 is a view of the CT image biopsy system of FIG. 15 afteradditional rotation.

FIG. 18 shows a translational stage for linear actuation of thehigh-resolution detector of the present invention.

FIG. 19 is a flowchart of a method of performing a simulated biopsyusing a CT scanner in accordance with the present invention.

FIG. 20 illustrates a schematic of the field of view of the CT imagebiopsy system of FIG. 15.

FIG. 21 is a schematic view of an apparatus for performing a CT imagedata-guided robotic biopsy.

FIGS. 22A and 22B are schematic views of the robotic assembly of theapparatus of FIG. 21.

FIGS. 23A and 23B are schematic views of an alternative robotic assemblyof the apparatus of FIG. 21.

FIG. 24 is a schematic view illustrating the degrees of freedom of therobotic assembly of FIGS. 22A and 22B.

FIG. 25 is a flowchart of the method of performing a CT imagedata-guided robotic biopsy in accordance with the present invention.

FIG. 26 is a schematic view of a breast restraint device in accordancewith the present invention.

FIG. 27 is a schematic view of a breast restraint device of FIG. 26 usedin combination with a biopsy needle.

FIGS. 28-30 illustrate alternative geometric configurations of thesuction cup of the restraint device of FIG. 26.

FIG. 31 illustrates a CT based radiation therapy assembly in accordancewith the present invention.

FIG. 32 shows the device of FIG. 31 through partial rotation.

FIG. 33 is a horizontal collimator assembly of the device of FIG. 31.

FIG. 34 is a vertical collimator assembly of the device of FIG. 31.

FIG. 35 is a schematic view viewed from the x-ray source of thecollimator assemblies of the device of FIG. 31.

FIG. 36 illustrates the view of FIG. 35 with an alternative 8-panelcollimator assembly.

FIG. 37 illustrates the view of FIG. 35 with an alternative 16-panelcollimator assembly.

FIG. 38 illustrates an ultrasound based therapy assembly in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring more specifically to the drawings for illustrative purposes,the present invention is embodied in the apparatus generally shown inFIG. 1 through FIG. 37. It will be appreciated that the apparatus mayvary as to configuration and as to details of the parts, and that themethod may vary as to the specific steps and sequence, without departingfrom the basic concepts as disclosed herein.

1. CT Imaging of Pendant Breast.

Referring to FIG. 1, a breast CT scanner 10 tailored specifically forbreast cancer screening is shown. The scanner has a padded table 12 witha circular opening 16 through which the patient may individuallyposition the breast to be screened. A CT scanning mechanism 18 ispositioned in chamber 20 under the table 12. The scanning mechanism 18comprises an x-ray emitter 24 and detector 26 supported on opposingsides of a rotating gantry 22. A centrally located motor 28 ismechanically coupled to the gantry 22 so that the gantry 22 is rotatedin the horizontal plane about axis 32 during operation. A chain linkconduit provides a flexible spiral linkage for cables 36 connected tothe gantry 22 and x-ray emitter 24 and detector 26.

FIGS. 2A and 2B illustrate the CT scanner 10 of the present inventionbeing used to capture CT images of a patient's breast 40. With thepatient lying prone on the table 12, the patient's breast 40 hangs in apendant position though opening 16 in depression 14 into chamber 20. Thegantry 22 rotates 360 degrees about the pendent breast 40, while thescanning mechanism 18 continually registers images as the x-ray beam 42emitted from emitter 24 passes through the tissue of breast 40. Thescanning mechanism 18 images at a rate of 30 frames per second, but mayalso image at faster or slower rates to accommodate the capture rate ofthe detector. The process takes about 17 seconds per breast to complete,but may vary to increase the number of captured images or lessen theamount of time the patient is required to remain still.

No breast compression is necessary when imaging with the breast CTscanner 10, and the radiation levels are substantially equivalent tolevels generated in typical mammography. The horizontal orientation ofthe scanner 10 also prevents the exposure of tissues in the thoraciccavity, because the CT is performed in the coronal plane. To ensure thatbreast tissues close to the chest wall and in the axilla are imaged, thex-ray emitter 24 and detector 26 are positioned just below the bottom ofthe shielded table 12. The table surface surrounding the opening 16 forthe breast comprises a depression 14 or swale to allow a portion of thechest wall to extend into the scanner field of view defined by beam 42and thus enable adequate coverage of the breast 40, as shown in FIG. 28.Gentle pressure beyond gravity would be applied to immobilize the breast40 and pull the breast tissue away from the chest wall, but the breastcompression used in mammography would not be necessary.

The coronal acquisition geometry of the dedicated breast CT scanner 10would allow the reconstructed CT images to be sized to the dimensions ofthe breast. For example, for a 15-cm-diameter field of view defined bythe beam 42, a 512×512 CT image would have pixel dimensions close to 300μm These dimensions may be manipulated according to the trade-offbetween image noise and voxel volume. Isotropic resolution (e.g., 300mm×300 mm×300-μm voxels), however, might be useful in concert withthree-dimensional viewing techniques and could be achieved by using conebeam techniques with flat panel detectors. For routine breast CTscanning, the section thickness probably would be on the order of 1-2mm.

The scanner 10 illustrated in FIG. 1 may also be used to image otheranatomical areas of interest of a patient. For example, the opening 16may be sized so that the patient may stand on the platform 30 to image aportion of the patient's leg. The platform 30 remains stationary whilethe gantry 22 rotates during imaging. This may be particularly useful incapturing CT images of a patient's knee under normal loading whilestanding.

2. Simulated Breast Compression.

The breast CT scanner, such as that shown in FIGS. 1, 2A and 2B,produces about 300 individual images per breast. Referring now to FIG.3, each image is a virtual coronal slice 50 through the breast 40. Asseen in FIG. 3, each of the vertical lines 52 indicates the area of thebreast 40 where each slice 50 was taken. In contrast, standardcompression mammograms are X-rays taken through all layers of the breastvia a projection imaging procedure utilizing relatively aggressivephysical compression of the breast. Because most radiologists currentlydiagnose breast cancer using mammography, they are accustomed to andtrained at viewing breast images which are mechanically compressed.Therefore, in order to compare the breast CT images with the moreconventional mammography images, it is desirable to present the imagesin the fashion with which radiologists are familiar.

Now turning to FIG. 4, a preferred method of the present invention usesa mathematical compression algorithm 62 to transform thethree-dimensional volume data set 60 generated from a breast CT scannerinto a compressed three-dimensional version simulating compression of abreast in a standard compression mammography image where the breast iscompressed between two parallel and opposed compression plates. Thecompressed volume breast data 60 is then projected onto atwo-dimensional image, or synthetic mammogram 66. The syntheticmammogram 66 is then compared to an actual standard compressionmammogram 68 from object (e.g., Mediolateral Oblique View (MLO) or theCranio-Caudal View (CC) compression mammograms) via comparison algorithm64. Based on defined goodness-of-match criteria, the comparisonalgorithm 64 will adjust a first of a plurality of parameters, repeatthe projection process to generate a new synthetic mammogram 66, andthen re-apply the comparison algorithm 64. This process continues untilthe goodness-of-fit criteria are met, wherein the algorithm saves thecompression parameters and presents the images to the observer forcomparison against the original projection images. This process isrepeated for each original projection image resulting in a series ofcompression parameters for each projection image to volume projection.

A more detailed view of the method of the present invention is shown inFIG. 5. The compression algorithm 62 takes the volume data 60 andcompresses it, determining compression parameters for the compressionwhich simulate actual physical compression of the breast duringmammography (either by mechanical modeling of the breast or by a simplegeometric distortion).

In the preferred embodiment, compression algorithm 62 incorporatesbreast tissue elasticity values to better simulate actual mammographycompression. Breast tissue elasticity may be further determined fromcompression and registration. Compression algorithms may also be basedon mathematical compression models and image registration models, orother methods incorporating physical and image parameters of volumebreast CT and projection radiographs.

After compression, the data is projected onto a two-dimension imageplane via a projection algorithm at step 70 to simulate an x-raymammogram and the resulting synthesized mammogram is registered to anactual mammogram at process block 71. The registration algorithm 62 mayemploy techniques including, but not limited to, one or more of thefollowing commonly used in the art: scaling, rotation, shifting,shearing and non-linear warping.

The synthesized and registered mammogram from process block 71 is thencompared to the actual mammogram at process block 64. Prior tocomparison, the mammography projection images 72 may be corrected andnormalized at step 74. The comparison may be made on the basis of imageinformation, such as the correlation of coefficient, energy, entropy orother similar methods commonly used in the art.

After the comparison algorithm 64, image match criteria are applied at76. If the image match criteria are met, the synthetic and mammographyprojection images are displayed at 78. If the image match criteria arenot met, the compression algorithm 62 is reapplied with at least one ofthe compression parameters and/or registration parameters being varied.

Referring now to FIG. 7, a compression algorithm 62 making use of anunderstanding of the physical structure of the breast is illustrated inmore detail. The volume data is first acquired in a volume imagingsystem (e.g., breast CT scanner) at step 80. The volume data may bepre-processed to stabilize and standardize the data. Concurrently orpreviously acquired projection images (e.g., CC and MLO views fromconventional mammography) are used for comparison, as shown in FIG. 6.In the present embodiment, the number of projection images employed isflexible and does not alter the basic functionality of the algorithm.

To assure proper operation of the algorithm, the data may be oriented toa standard orientation (e.g., nipple down, to the right, etc. with thebreast base at the top, left, etc.) The different types of breast tissue(e.g., skin, fat, glands, tumor, etc) are then segregated for example byuse of a histogram of the data and morphological filters (such aserosion) described herein. At process block 84 and 86, empiricallyderived mechanical and compression properties are then assigned to eachof these tissue types and a model of the breast is constructed, forexample using finite element techniques.

At process block 88 the data is oriented with respect to the actualmammogram to which the data will be compared and at process block 90 avirtual compression of the finite element model is applied.

Volume data are then projected in the direction of the z-axis onto animage plane at 70 by summation along the projection path of each voxelin the volume data set as distorted by the displaced locations of theelements of the compressed finite element model. Summation of the voxelsis determined by the voxel value (i.e., density, etc.) and a summationintegral that may evaluate the attenuation (e.g., x-ray, optical, etc.),transparency, or some other parameter to arrive at the projected valuealong the ray.

The algorithm may further transform the contrast properties of thevolume data to better match the projection contrast properties of themammography projection images 72. For example, the CT data set acquiredat relatively high kVp (x-ray beam energies) may be transformed tosimulate the low x-ray beam energies exemplary of mammography scans.With the known composition of each voxel in the three-dimensional volumedata set, linear attenuation coefficients at the lower x-ray energiesrepresentative of mammography may be used.

Coordinate alignment can be performed between volume projection andmammogram(s) to co-locate lesions in both data sets, either a lesionseen in a mammogram to a position in volume, or a lesion seen in volumeto a position in a mammogram.

Referring still to FIG. 7, the resultant projected image from step 70 isthen registered at step 71 and compared to the projection image based onone or more of a plurality of parameters at step 64 (e.g., differenceerror, correlation coefficient, mutual information, entropy, etc.). Ifthe images match within the specified criteria, the algorithm proceedsto step 78 and the image is displayed. Once the extent of compression tomatch images is obtained, the elastic parameters for each voxel areupdated to those calculated by the compression algorithm. Other means ofdetermining compression commonly used in the art may also be employed toaccomplish this part of the algorithm.

If the images do not meet the specified criteria, the algorithm iteratesby making a small adjustment in one of the compression or orientationparameters and repeats the process. This process continues until thespecified criteria are met. In a purely geometric implementation of thecompression algorithm, compression in the form of a geometric warp isapplied in the base direction. If fit criteria are not met at step 98,the compression is varied until the fit criteria are met. Each remainingZ level is optimally warped until the entire compressed volumeprojection matches the conventional projection image. The process isrepeated for each conventional projection view. Once completed, thefinal compression parameters are saved for viewing at step 78. Themathematical compression techniques of step 62 may take the form ofaffine transforms, or any number of other mathematical algorithms whichcan (linearly or nonlinearly) mathematically distort the breast from theuncompressed (x, y, z) to the compressed (x′, y′, z′) format.

In both types of compression, the compression parameters are saved asboth a forward and backward set that fully characterizes therelationship between the volume data and the projection data.

Referring now to FIG. 6, the present invention may display the CTacquired volume data in a variety of forms. In one embodiment, athree-view orthogonal display 51 provides a simultaneous presentation ofan axial image 51 a, a coronal image 51 b, and a sagittal image 51 c,each of which provide a user selected slice of data along the associatedcoronal, sagittal and axial planes. In addition a volume rendered image61 in any of these planes (sagittal shown) may be provided that combinesdata of the volume data from many slices or from a single slice ofvariable thickness to produce a simulated radiographic projectionthrough the uncompressed breast. The data of the volume rendered image61 may be subject to a different weighting systems as selected by theuser including a simple summation of the data along the rays ofprojection or a selection of the maximum value of data along theprojection, etc.

As shown, the axial image 51 a, coronal image 51 b, and a sagittal image51 c may be optionally aligned each to share one image axis, forexample, with the axial image 51 a positioned above the coronal imageSib, and the sagittal image 51 c positioned to the right of the coronalimage 51 b. In this way, a given location 53, having a unique x, y and zcoordinate within the volume data of the breast, can be highlighted witha cursor 57 on each of the orthogonal axial image Sla, a coronal image51 b, and a sagittal image 51 c. An optional vertical alignment line 54connecting the locations 53 in axial image 51 a and sagittal image 51 c(showing the plane of the slice of the coronal image 51 b), and anoptional horizontal alignment line 55 connecting the locations 53 in thecoronal image 51 b and the sagittal image 51 c (showing the plane of theslice of the sagittal image Sic) can also provided, each line 54 and 55flanked by parallel lines 54′ and 55′ respectively showing the thicknessof the given slices.

In addition, a synthetic mammogram 66 a may be presented showing thesagittal view of the breast with virtual compression, as describedabove, to simulate an actual mammogram 68 a, which may also bedisplayed. A cursor 57 may also be marked on the synthetic mammogram 66a corresponding to locations 53 in the axial image 51 a, coronal image51 b, and the sagittal image 51 c using the mapping described by theforward and backward set characterizing the relationship between the CTvolume data and the projection data described above. A similar cursor 57can be placed in the same location on an actual sagittal mammogram 68 apreviously acquired on a separate mammography machine and based on thematching done between the synthetic mammogram 66 a and the actualmammogram 68 a, as described above.

In addition to synthetic mammogram 66 a in the sagittal plane, an axialplane synthetic mammogram 66 b may be provided and optionally matched toan axial compression mammogram 68 b previously acquired on a separatemammography machine. In addition, multiple coronal slice images, forexample, slices 50 a, 50 b, and 50 c may be provided and, in each ofthese images, corresponding cursors 57 located to move with the cursors57 in the other images. Each of the images may be moved and rotated withcorresponding movements and rotations being automatically effected inthe other images.

By allowing the cursors 57 to move in tandem under the guidance of anoperator, the same location 53 may be pinpointed in all displayed imagesand a simultaneous computation and optional display of actualcoordinates 58 of the location 53 may be provided as can be used inguiding a virtual or actual biopsy. This common interactive cursor 57allows the operator to co-locate lesions and other structures present inany of the images to the location of all other images. Sinceradiologists typically only have experience in viewing breast images inthis compressed projection imaging format, it is highly desirable todevelop this viewing technique for radiologists to learn and make use ofbreast CT images.

Each of the images can be freely manipulated on the display 59 asindividual windows per conventional techniques and arranged for theconvenience of the operator. Lightness, contrast, magnification andorientation of each of the images may be freely adjusted andconventional tools allowing for measurement of areas, lengths, andvolumes on the images may be provided according to techniques well knownin the art. These tools may also provide for histograms or otheranalysis of the underlying data of the images within regions selected bythe operator. Thus a lesion can be identified using not only visualinspection of the images but also by computer analysis of image/volumedata with respect to density, geometry, roughness, architecture, andmore, as guided by the user.

The display 59 may further provide a set of user manipulatable controls67 allowing control of the location of the cursors 57 (or direct controlof the cursor 57 by dragging the cursor on any image), an amount ofmagnification of the image, and the thicknesses of the slice of datafrom which the volume rendered image 61 is created. Given images may bestored and accessed by “snapshot” icons 63 storing the image parametersand pointing to the correct data so as to allow that image to berecreated and yet further manipulated. For slice images, the slice maychange as the cursor location is moved, so that a slice holding thecursor is always displayed.

A region of interest control 69 allows creation of a region of interestwithin the displayed data generally defining a bounded volume around thecursor 57 and that data to be individually viewed and manipulated. Thistool allows isolation of the volume data related to the lesion toprovide a virtual “electronic scalpel”. By removing this region from theimage, or by removing image data surrounding the region, the region maybe better examined. The region and non region data may be processeddifferently to accentuate these differences. Further, the underlyingdata as segregated may be quantitatively processed to characterize thetissue to the operator.

The image manipulation and fitting technique described above, whichallows matching of mammography data to the tomographic data, can also beused to match tomographic or mammographic data taken over time in, forexample, a longitudinal study. Using the compression parameters used ingenerating the synthetic mammogram, the operator can co-locate lesionsor other structures present in the mammogram in all other images. Sinceradiologists typically only have experience in viewing breast images inthis compressed projection imaging format, it is highly desirable todevelop this viewing technique for radiologists to learn to make use ofbreast CT images.

3. Breast Density Evaluation, Risk Prediction, and Personal Screening.

Breast density refers to the amount of glandular tissue in a woman'sbreast, and typically younger women have higher degrees of glandularity,with glandularity becoming reduced in postmenopausal women. It has beendemonstrated by other researchers that women with higher breast density(increased breast glandular component) have a higher probability ofgetting breast cancer. Thus, in routine breast CT scanning, theevaluation of breast density can be used as a measure of subsequentrisk, and could in fact be used to tailor individualized risk-basedscreening approaches for each individual woman. In mammography,assessment of the fraction of the breast that is glandular is difficultbecause the tissues are all superimposed onto each other.

Breast CT, by virtue of the fact that the volume data set of imageseliminates overlapping tissues, enables the direct calculation of breastdensity. Automatic algorithms are used to produce accurate measurementsof breast density from the breast CT volume data set, and thesemeasurements could play an important role in the medical and riskmanagement of individual women.

FIG. 8 illustrates a sample of twenty-four breast CT images 120 out ofthe approximately 300 images produced by typical breast CT of onebreast. The breast images 120 demonstrate coronal views of the breastfrom the base of the breast (upper left) to the nipple (lower right).FIG. 9 shows an exploded view of one of the images 120 which generallycomprises a dark or black shade (corresponding to air) surrounding thebreast and the breast, which shows a high density (white) skin-line 126,darker (grey) non-glandular, or adipose tissue 124, and the glandulartissue 122 interior to the breast (which appears white).

The volume data set in CT is an accurate depiction of the x-rayproperties of the breast throughout the volume of the breast. Each 20coronal CT image 120 is comprised of individual pixels, each with anarea given by the dimensions of the (x, y) pixel(Area=δ_(x)×δ_(y)). Theimage also is characterized by a “section thickness,” which can becalled δz. These concepts are well known to those skilled in the art ofCT. The volume of each volume element (“voxel”) is then:V _(voxel) =δx×δy×δz.

In one embodiment of the present invention, the total breast tissuevolume can be segmented using the method illustrated in FIG. 10. First,the two-dimensional CT images generated at step 130 are processedaccording image intensity at step 132. For example, a histogram shown inFIG. 11 may be generated corresponding to the breast CT image of FIG. 9.The ordinate axis represents the number of pixels, and the abscissarepresents the grey scale value. The left peak 150 corresponds toadipose tissue 124, and the right peak 152 corresponds to glandulartissue 122. Thus, data points to the left of threshold value T2 aremostly outside of the breast (due to their low image densities), andthose voxels of the image that have a gray scale greater than T2 areconsidered to be inside the boundaries of the breast. The total numberof voxels “inside” the breast can be found at step 134 by summing theimages from each image over the total number of images in the volumedata set. The number of voxels inside the breast N_(breast), can then bemultiplied by the voxel volume V_(voxel) to determine the entire breastvolume at step 136 with the equation:V _(breast) =N _(breast) ×V _(voxel)

To identify the volume of the breast that is comprised of glandulartissue, the same procedure as that outlined in the above paragraph canbe used, except that the threshold value T1 is used instead of T2.Voxels having gray scale values above T1 (for example) are not only“inside” the breast, but are also very white voxels as seen in the image120, and therefore these voxels are those which are predominantlycomprised of glandular tissue. The total volume of glandular tissueV_(gland) in the breast is determined by segmenting the pixels abovethreshold T2 at step 138 to find the number of glandular pixelsN_(gland) and then multiplying the number of identified pixels by thevoxel volume at step 140 with the equation:V _(gland) =N _(gland) ×V _(voxel)

The breast density, β, can then be computed at step 142 as the fractionof the volume of a woman's breast which contains glandular tissue,expressed as:β=V _(gland) /V _(breast)

Other variations of the above equation may exist and may be useful incharacterizing what is known subjectively in the clinical environment as“breast density”.

The above breast density calculations may be further manipulated togenerate risk assessments in a breast cancer screening regime forindividual patients. Since women with higher breast densities are knownto have a higher incidence of breast cancer, it is logical thatheightened screening procedures (different breast cancer screeningtests, more frequent tests, or combinations of different screeningtests) would have a higher probability of discovering breast cancer atan earlier stage.

Breast density calculations may be performed on a number of womenspanning the age of breast cancer screening, for example from 40 yearsto 90 years of age. The mean breast density X_(BD) can be determined fora large number of women in each age group (e.g., every 5 years). Themean breast density X_(BD) and the standard deviation in this value QBDcan be used to assess the relative breast density of each woman,relative to women in the same age range. Simple statistical tests (suchas the student's t test) can then be used to evaluate z-scores, whichwould establish how well a woman's breast density matches the norms forher age. Women with higher breast density levels would then beconsidered to have higher risk factors for breast cancer.

FIG. 12 shows the hypothetical relationship between breast density andage. These data, which can be generated after enough patients arestudied by our breast CT scanner, can then be used to assess therelative (age-adjusted) breast density value for an individual woman.

Histogram-based voxel segmentation can also be replaced or augmented byspatially-based methods for pixel segmentation. For example, standardlinear (e.g., convolution or enhancement filters) and non-linear (e.g.,non-convolution or morphological filters) image processing techniquescommonly used in digital image processing applications may be used atstep 132 in combination with histogram methods. Both techniquesaccomplish their results by examining and processing an image in smallregions, called pixel “neighborhoods.” A neighborhood is a square regionof image pixels, typically 3×3, 5×5 or 7×7 in size.

For example, simple linear smoothing procedures can be used at step 132to smooth the image prior to histogram analysis. Enhancement orconvolution filters process image neighborhoods by multiplying thevalues within a neighborhood by a matrix or “kernel” of filteringcoefficients (integer values). The kernel is the same size as theneighborhood that it is being applied to. The results of thismultiplication are summed and divided by the sum of the filter kernel.This result then replaces the center pixel in the image neighborhood.For example, a low-pass, gauss or median filter may be used to eliminatedetail or random image noise in preparation for segmentation.

Non-linear or non-convolution techniques may also be applied to theimage. Unlike convolution filters, they do not multiply the neighborhoodvalues by a kernel of filtering coefficients. Instead, a non-convolutionfilter works only with the data in the neighborhood itself, and useseither a statistical method or a mathematic formula to modify the pixelupon which it is focused.

An erosion filter is an example of a non-linear enhancement techniquethat may be used to eliminate the skin boundary from the image. Anerosion filter changes the shape of objects in an image by eroding(reducing) the boundaries of bright objects, and enlarging theboundaries of dark ones. The skin boundary, which is not glandulartissue, has gray scale values similar to glandular tissue, and thus canintroduce error in determining glandular tissue density. By eroding theskin, only the actual breast tissues would be evaluated in theassessment of breast density, and this process would reduce theconfounding nature of the skin voxels in the calculation of breastdensity. Erosion or other image processing techniques (such as linearSobel or Roberts edge filters) may be used to essentially redefine theborder of the breast tissue volume some finite distance (e.g. D_(skin))from the air-skin boundary.

Thus, Breast CT genuinely enables the calculation of breast density dueto the three-dimensional volume data set that is reconstructed with thistechnology. It is envisioned that the automatic algorithms can be usedto produce accurate measures of breast density from the breast CT volumedata set, and that these measures could play an important role in themanagement of individual women.

Although the density and volume measurements are ideal for determiningbreast density, the methods of the present invention may be used fordetermining volume and density of a number of anatomical features of thepatient.

4. CT Image Biopsy.

While the breast CT scanner is capable of high-resolution computedtomography scanning, an apparatus of the present invention useshigh-resolution techniques to replace physical (needle-core) biopsies.If imaged with sufficient spatial resolution, it is anticipated that theimage data itself can serve as an imaged-based biopsy for some women,and this would obviate the need for mechanical insertion of a needleinto the woman's breast.

FIGS. 13 and 14 illustrate the typical geometry of a breast CT scanner10 of FIG. 1, with the breast 40 positioned between the x-ray source 24and the detector 26. The breast 40 is depicted as a cylinder, and theshadow 44 of the breast is projected onto the x-ray detector 26 as arectangle in FIG. 13. FIG. 14 illustrates the top-down view of thebreast CT scanner 10, with the x-ray source 24 and detector 26 rotatingaround the stationary breast 40 during the acquisition sequence.Normally, a 360 degree image acquisition is obtained. Generally,detector 26 comprises a 1024×768 matrix (using 2×2 binning) toreconstruct the three-dimensional volume dataset (approximately 300images, each with 512×512 matrix size). The voxel size of each pixel isapproximately 0.20 mm to 0.30 mm. When a suspicious lesion or area inthe breast 40 is identified by the diagnostic physician, in mammography(for example), additional views including magnification views areacquired.

Referring now to FIG. 15, a CT image biopsy system 170 in accordancewith the present invention is shown. The CT image biopsy system 170 isconfigured to generate a high-resolution image of a suspicious region ofinterest (ROI) 174 in the anatomy of the patient, e.g., a suspectedcancer region in the patient's breast 40. By obtaining a focused, veryhigh spatial resolution image where the suspected lesion 174 is thoughtto occur, a dramatically increased diagnostic potential, approachingthat of a needle core biopsy (currently the state-of-the-art for breastcancer definitive diagnosis) may be achieved.

To generate the high-resolution image, a high-resolution detector 172(e.g., 2048×2048 matrix with 25 μm pixels) is imposed in front (on thex-ray source 24 side) of the breast CT scanner detector 26. For thepurposes of this invention, the high spatial resolution detector system172 for CT image biopsy may comprise a charge couple device (CCD), aceramic metal oxide semi-conductor (CMOS), a high spatial resolutionsmall field of view thin-film transistor (TFT), or any high resolutionx-ray detector system currently used in the art for x-ray acquisition.

Alternatively, the high-resolution detector may be an indirect detectorsystem, where a scintillator, such as Cs1, GD02S2, LaAOBr, Y2T04, etc.,is used to convert the incident x-ray beam into light to be subsequentlydetected by the optical detector system. In another embodiment, a directdetector system may be used, which results in the direct conversion ofthe x-ray ionization of the detector components into an electronicsignal that is amplified and digitized for image formation. Examples ofdirect detector systems include lead oxide, mercuric oxide, selenium,and other such systems known in the art.

The CT image biopsy system 170 further includes a collimator 176 tofocus the wider x-ray beam 42 emitted from source 24 to a narrow fieldof view 178. By focusing the field of view, the system 170 onlyinterrogates the suspicious region 174 in the breast 40, which isreceived by the high resolution detector 172. This careful collimationis not only beneficial in reducing the radiation dose to the patient,but also in reducing the amount of x-ray scatter that is imaged.

Referring now to FIG. 16, the high-resolution detector 172 andcollimator 176 may be configured with additional motion components toadjust the position of the high-resolution detector 172 and collimator176 during the CT acquisition, depending upon where the identifiedlesion was in the volume dataset. If the region of interest 174 isexactly at the center of the breast 40, the high-resolution detector 172and collimator 176 remain stationary with respect to the rotatinggantry. However, when the region of interest 174 is located at theperiphery of a large breast, the high-resolution detector 172 andcollimator 176 move in a sinusoidal fashion as the breast CT gantryrotates around the 360 degrees of motion to intercept the collimatedx-ray beam 178.

FIG. 16 illustrates that, during rotation of the CT gantry, the positionof both the collimator assembly 176 and the high-resolution detector 172shift in the X direction (see FIG. 13) in order to remain in the directx-ray shadow of the region of interest 174. The geometry of the system170 geometry dictates that the motion of the high resolution detector172 relative to the low resolution detector 26 (which is fixed to thegantry) will involve a sinusoidal motion, both in the x (lateral) and z(azimuthal) directions for a region of interest 174 that is off-center.The collimators 176 will also follow the sinusoidal motion (e.g., withadjustable collimator jaws), albeit with less amplitude due to thegeometrical demagnification. By moving the high-resolution detectorsystem in a sinusoidal motion, the same volume of tissue is imaged overthe entire 360-degree scan.

FI 17 illustrates yet another view of the high resolution CT imagebiopsy system 170, having rotated through a larger angle than in FIG.16. Note that both the collimator assembly 176 and high-resolutiondetector 172 have moved to keep co-linear with the suspected lesion 174.

FIG. 18 illustrates an actuation system 180, as viewed from the x-raysource, configured to enable the sinusoidal motion of thehigh-resolution detector 172. The high-resolution detector 172 has alead backing 182 to prevent the excess (penumbra) x-ray field fromstriking the primary breast CT detector 26. To accommodate linear motionin the x-axis (affecting a corresponding sinusoidal motion as the gantryrotates through its range of motion), a worm-drive system may beemployed using lead screws 184 and motor-controlled housings 186 todrive the lead screws 184. The lead screws 184 allow the motion of thehigh-resolution x-ray detector 172 and its backing 182 to move laterally(i.e. the along the x-axis) across the field of view under the computercontrol. A second set of lead screws 188 may be positioned perpendicularto the horizontally-oriented lead screws 184. The vertically-orientedlead screws 188 are controlled by a second set of motor housings (notshown) to allow the vertical positioning (in the z-axis) of thehigh-resolution x-ray detector 172.

Alternative embodiments of the CT image biopsy system 170 may includethe use of cables (or wires) transported by motor-controlled pulleysystems to effect motion of the high-resolution x-ray detector 172 inboth the horizontal and vertical directions. Other positioning systems,such as pneumatic positioning systems, systems based upon linear motortechnology, or other mechanical devices for translation in one or moreaxes may also be used.

A further alternative mode of scanning may include the use of astationary x-ray detector with an x-ray focal spot which moves in atranslational matter in both the horizontal and vertical dimensions.Similar means for motivation (e.g. lead screws, linear motors,cable/pulley systems, etc.) can be envisioned for the motion of thex-ray source or collimators 176.

Referring to FIG. 19, a method for performing a simulated, or “virtual,”biopsy using a CT scanner is described. First, a scan (step 201 in FIG.19) of the anatomical region, e.g., the patient's breast, is made usinga normal resolution scan on a primary CT detector, (e.g. the 1024×768detector 26 in FIG. 17). The normal resolution breast CT image data isthen used to indicate the specific location that is considered abnormaland in need of further follow up at step 203. A three-dimensional cursorsoftware, or other algorithm based upon basic geometry, may be used totriangulate upon the coordinate in the breast 40 identified by theradiologist as a region of interest or suspicious lesion breast CTimages.

Once a region of interest is located, acquisition of a very high spatialresolution breast CT is performed by imposing a second detector, e.g.,the high spatial resolution detector 172, into the field of view of theCT scanner (step 205), and then scanning the region of interest onto thehigh resolution detector (step 207). During scanning, a computeralgorithm may also control the motion of the high-resolution detectorand x-ray source, according to the identified location of the region ofinterest, to maintain focus of the x-ray beam and subsequent detectionon the region of interest. After acquisition of the high resolution CTdata, further processing is performed (step 209) to reconstruct theimage for display.

For breast CT, the spatial resolution of the reconstructed volumedataset depends upon a number of parameters, including the focal spotsize, the reconstruction matrix, the mathematical filter, the number ofviews acquired, and the spatial resolution of the imaging detector. Oneor more reconstruction algorithms may be employed to condition themoving source geometry relative to the moving detector geometry. Thereconstruction algorithm may facilitate placement of the detectedhigh-resolution data in a larger matrix projection image (e.g., from theprimary, normal-resolution CT detector), and adapt it for the sinusoidvariation of the location of the high-resolution image in terms of itsplacement into the larger matrix projection image. Generally, only theregion corresponding to the high-resolution biopsy zone isreconstructed. To fill in the data set outside of the high-resolutionimage data (in the larger matrix), projection image data from thelow-resolution scan is used. Thus, lower resolution CT scan data forboth positioning data and to correct for breast tissue which is outsidethe field of view of the high-resolution scan. This provides the entireview for the mathematical filtering operation that is used for CTreconstruction.

In general, the high resolution CT image biopsy acquisition sequence maybe accompanied by higher exposure rates (increased exposure per frame)and a larger number of acquired views to achieve the higher spatialresolution desired to simulate biopsy of the suspect or target tissue.The reconstruction of the high resolution CT image biopsy volume datasetwould also accommodate the position of the detector (or x-ray source ifit is being moved), using geometric corrections commonly used in theart.

Referring to FIG. 20, additional operations may be performed to correctfor artifacts resulting from the high resolution scan. Because the x-raybeam that is focused on the high spatial resolution detector 172interrogates tissue that is excluded from the cone beam projection imagedataset, artifacts may result in the reconstruction of thehigh-resolution volume dataset. Since the high resolution CT imagebiopsy is acquired after the acquisition of the normal breast CT image,the additional information needed to correct the high-resolution volumedataset may be supplied by the initial, low-resolution breast CT scandata. The projection integrals associated with the cone beam projectiondata for the normal (low resolution) CT datasets may then be subtractedfrom the high resolution CT reconstruction (for the CT image biopsy), toremove the peripheral information which would lead to artifacts. In thecontext of FIG. 20, a line integral is projected through the imageduring filtered back-projection. The projection value P is equal to thesum of the components (A+B+C). Thus, to correctly use the projectionvalue C across the field of view of the CT image biopsy, the values of Aand B may be determined from the reconstructed low-resolution image,whereas C is computed directly.

Using this type of acquisition, it is anticipated that much higherspatial resolution (perhaps 100 micrometers) may be achievable.

The high-resolution CT image biopsy will provide the additional spatialand contrast resolution (due to the higher spatial resolution of thedetector, and the increased radiation levels used to acquire this CTimage dataset) to enable diagnosis in regards to breast cancer withincreased confidence. The existence of this technology may reduce oreliminate the need for physical forms of biopsy (e.g. incision or needlecore biopsy). In addition, it is appreciated that the above methods andapparatus may be used in a number of applications beyond scanning breastlesions. For example, CT image biopsy may be performed on otheranatomical regions of interest on the patient wherever traditionalbiopsy would be performed.

5. Physical Robotic Biopsy.

The CT scanner 10 of FIG. 1 provides exceptional spatial localizationcapabilities. Consequently, CT image data may be used for performing ahigh precision and high accuracy biopsy of small tumors using aphysician-guided robotic system.

A schematic view of the robotic biopsy system 200 of the presentinvention is shown in FIG. 21. The robotic biopsy system 200 consists ofseveral modules, including: a volumetric data physician targeting module202, a command and control module 206, a robotic assembly module 208,and a deployable biopsy/therapy/procedure module. The volume dataset 210from the CT scanner is input into the targeting module 202 fordetermination of the lesion location 214. With the target location 214determined, the control module 204 provides the physician with aninterface that intuitively translates lesion coordinates into thedesired motion(s) of the robotic assembly 206 for optimization of needletrajectory to the target lesion site. The robotic assembly 206 is small,and sufficiently robust to support a biopsy device that will penetratethe skin and be accurate under load so that positions are rigid andknown. The robotic assembly 206 also is radiolucent and yet strongenough to support the range of desired functional operations.

The targeting module 202 and control module 204 are tightly integratedwith the scanner hardware and software so imagery is directly availablefor robotic guidance and localization verification. A positionmonitoring and correction module may also be incorporated to monitor themotion of the robotic assembly 206 and correct the motion according toinput by the physician. After the robotic assembly 206 has beenpositioned to the proper location, the biopsy/treatment module 208deploys to administer the biopsy or deliver therapy at the targetlocation within the breast 40.

FIGS. 22A and 22B illustrate a preferred embodiment the robotic assembly206 based on a horseshoe design that pivots upwards and rotates aroundthe scanner's is rotational axis 32 (see FIG. 1) to align the biopsydevice with the sampling location 214. The robotic assembly 206 includesa horseshoe-shaped positioning arm 222 that is pivotably mounted to arobotic support platform 224. The robotic support platform 224 isconfigured to be pivotably mounted to the platform 30 (see FIG. 1) ofscanner 10 to facilitate rotation of the robotic assembly about thegantry rotation axis 32. The positioning arm 222 is configured tosupport manipulator 226, ideally allowing the manipulator to move infour degrees of freedom (DOF), described in more detail with respect toFIG. 24 below. The manipulator 226 is configured to house treatment arm228, with manipulator 226, at least allowing linear motion of thetreatment arm 228 with respect to the manipulator 226. The treatment arm228 releasably retains treatment instrument 230, such as a biopsyneedle, for treatment at the target location. The releasability of thetreatment arm's retention of the treatment instrument 230 allows for thetreatment instrument 230 to be switched out or cleaned between patients.

FIGS. 23A and 23B illustrate an alternative embodiment of a roboticassembly 240 that incorporates a suspended mount. The robotic assembly240 has a carriage mount 242 that is configured to mount around opening16 of CT scanner table 12. The carriage mount 242 is coupled to ahorseshoe-shaped positioning arm 246 via gantry drive motor 244. Thegantry drive motor 244 facilitates motion of the positioning arm 246about the gantry rotation axis 32. The positioning arm 246 is furtherconfigured to house biopsy manipulator 248 via a manipulator drive motor250 that allows the manipulator 248 to travel along the track of thehemi-spherical positioning arm. The biopsy manipulator 248 is shown in avariety of positions in FIG. 23A and at both 0° and close to 90°positions with respect to the carriage mount 242 in FIG. 23B. Cables 252connect the drive motors to the control module 204. It is appreciatedthat motion may be facilitated in robotic assemblies 206, 240 by avariety of actuator means, including servo motors, linear actuators, orlike devices commonly available in the art.

The breast CT scanner gantry 22 (see FIG. 1) and the robotic assemblies206, 240 move independently of or in synchrony with each other, makingit possible to acquire and use 3D image data to track, correct andperfect needle insertion during procedures.

The breast CT scanner 10 rotates about the breast 40 in an unobstructedcylindrical workspace with an inner diameter of approximately 75 cm. andan outer diameter of approximately 95 cm. The inner diameter of thiscylindrical workspace is defined as the distance from the CT source 24to the CT detector 26. Although this distance is adjustable, its lowerbound of 75 cm. was chosen so as to optimize the tradeoff of imageresolution and height/cost limitations of the detector.

The height of the cylindrical workspace is defined as the distance fromthe patient table 12 underside to static platform 30 immediately abovethe rotating armature 22 supporting the CT source 24 and detector 26.This distance is also adjustable to accommodate breast size variations,but a lower limit of approximately 40 cm. has been found to be optimal.Therefore, the available design space for the proposed robot assembly isa cylinder of 75 cm. diameter and 40 cm height, minus the hemisphericalvolume occupied by the patients breast, i.e., the biopsy space.

The CT scanner gantry 22 encompasses the robotic assembly 206, insteadof visa versa, for two reasons: first, the more proximal the roboticassembly 206 is to the biopsy space 214, the greater its stability andprecision; and second, the robotic assembly 206 materials are selectedto minimize x-ray absorption so that the breast 40 can be imaged withthe robotic assembly 206 deployed. In this configuration, the roboticassembly 206 partially obstructs the C projections, so radiolucencymakes it possible to obtain views during biopsy device deployment withminimum attenuation artifacts. Partial acquisition reconstruction mayalso be used to reduce reconstruction artifacts and optimize imagequality and robotic feedback and guidance data.

Referring now to FIG. 24, the robotic assembly 206 has one axis ofsymmetry (the scanner central axis 32) and in the preferred embodimentprovides at least five degrees of freedom. The robotic assembly'sdegrees-of-freedom are as follows: 1) rotation about scanner axis 32 isfacilitated by rotation of the robotic support platform 224 about thegantry platform 30; 2) elevation of the support arm 222 upward from therobotic support platform 224; 3) elevational angulation of manipulator226 with respect to the support arm 222; 4) lateral motion of themanipulator 226 across support arm 222; 5) lateral rotation of themanipulator 226 with respect to the support arm 222; and 6) biopsyneedle insertion 230 via linear motion of treatment arm 228 with respectto manipulator 226. It will be appreciated that a number of differentcombinations of robotic assembly's degrees-of-freedom may be achievedthrough the separate robotic linkages. For example, the treatment arm228 may rotationally articulate laterally (and vertically) with respectto the manipulator 226 in addition to, or in replacement of, the sameangular articulations of manipulator 226 with respect to the support arm222.

The robotic assembly 206 provides all needle 230 movements required in acomplete breast biopsy exam. The range of desired needle placementmotions is as follows:

-   -   Primary needle placement is concerned with being able to point        precisely to the center point of the biopsy space 214 from any        point within the biopsy space. This capability is most critical        and has spherical symmetry that is exploited by the robotic        assembly's design.    -   Secondary needle movement provides the ability for a lateral        displacement to move laterally away from a given primary needle        placement. (e.g. up to +/−10 cm.).    -   Tertiary needle movements are angle orientation changes of the        needle from a given secondary needle placement.    -   Needle trajectory is optimized to minimize lateral forces on        biopsy device. Fine adjustment of the needle position and        orientation may be made after coarse positioning is completed.

FIG. 25 illustrates a preferred method of the present invention forperforming a biopsy (or other treatment) on a patient via a CT imagedataset-guided robotic assembly. In a preferred embodiment, thegenerated volume data set (step 260) is used to localize an area ofinterest (i.e. lesion, suspicious object, mass, etc.) under physiciandirection (step 262). Three-dimensional coordinates are determined andcorrected to the calibrated reference frame of the object (or patient)at step 264. The multiple view display with co-locating cursor andsimultaneous display of actual and synthesized mammogram can be used inidentifying the three-dimensional coordinates. For example, using theguidance of the standard mammogram, a cursor can be located in threeorthogonal views or on a slice of a multiple slice display to uniquelyidentify x, y and z coordinates.

An optimized targeting algorithm then determines the trajectory tominimize tissue distortion or damage and avoid intersection withcritical structures at step 266. The trajectory algorithm may employstructure avoidance, minimum path, and motion tracking and correctionmodules to optimize the trajectory.

A control/deployment algorithm then computes the sequence of motionsnecessary to translate the trajectory into robotic motions at step 268.The control algorithm translates x, y, z coordinates of the lesionderived from the volume data into direction and trajectory instructionsfor the robot to optimize approach as defined by the physician viewingthe original volume data. For example, the control algorithm may employJacobian transforms to transform commands from Cartesian space to jointspace. Alternatively, the computer can drive the needle all the way tothe suspected lesion under image-guided control.

The robotic assembly deploys at step 270 along the path defined toarrive at the optimized position of the platform. Movement of therobotic assembly is therefore precisely controlled. Linear motion isemployed for final device or needle deployment to utilize needlerigidity and minimize tissue trauma. Visual feedback (video, ultrasound,and volume images) and deformation of tissues are monitored at step 276and provided to the operator to monitor deployment, and correct fortrajectory in real-time. In particular, an ultrasound imaging probe mayprovide additional trajectory verification. Analysis software providingcompensation for tissue distortion during deployment may also be used.After arrival at the proper position, the operator is notified. Thebiopsy/therapy device is deployed at step 272 once the operator givesthe device the validation command. When the procedure has beencompleted, the biopsy/therapy device is retracted at step 274 and thenthe robot assembly is moved to its parked position.

The well-defined geometry of the scanner and the shape of the pendantbreast provide several design advantages compared to conventionalrobotic design: first, the geometry is relatively compact, improvingstability of the robot; and second, the azimuthal symmetry of thependant breast facilitates biopsy access from all orientations aroundthe breast central axis. The design all of all mechanical parts in therobot workspace have minimum displacements of the biopsy needle duringpositioning and insertion.

The robotic assembly provides a stable platform for breast biopsy thatis not distorted due to loading on the robot, either from weightconsiderations or reactive force to needle insertion. Thus all of themotions of the robot are guided by optimizing needle or deviceorientation prior to insertion. The net performance of the robot forbreast biopsy is a system capable of positioning a needle to within 1mm. of a defined target.

A physician guided, computer stabilized and image-guided biopsy systemprovides a more accurate, rapid and less traumatic biopsy of breasttissue, thus producing a very positive impact on early detection andmanagement of breast cancer. Thus, integration of high resolutionvolumetric breast imaging, image guidance algorithms and medicalrobotics makes possible more precise biopsy sampling that enhances thephysician's ability to locate lesions on the scale of 2-3 mm. indiameter and extract breast tissue samples from those lesions with aconsistently high level of precision. Additionally, the increasedprecision resulting from these techniques also paves the way for otherminimally invasive therapy strategies.

The geometric accuracy of the CT machine can be improved by scanning aphantom having radio-opaque markers (small metal beads) aligned alongthe axis of rotation of the scan offset from that axis. The scanproduces a number of projection images over 360 degrees of scanning, andsequential images are analyzed to establish a track showing apparentmotion of the markers between images. These tracks can be describedmathematically as ellipses and analyzed to reveal characteristics of thegeometry of the scanner that are otherwise hard to measure (e.g., theexact location of the focal spot of the x-ray tube within the tubeenvelope). Knowledge of the geometrical aspects of the scanner allowsbetter determination of actual coordinates from image data. Geometricdistortions are also accommodated to some degree by the ability to imagethe robotic biopsy systems with the same scanner before and during thebiopsy procedure. Any geometric distortion applies to both images, thusdecreasing its effect on biopsy needle placement.

6. CT Breast Scanner with PET.

One advancement in locating malignant tumors in the body has been thedevelopment of PET (Positron Emission Tomography) scanners. PET is anuclear medicine technology that uses radioisotopes to allow thenoninvasive diagnostic imaging of metabolic processes in various organsystems of the human body. Images are obtained from positron-emittingradioactive tracer substances (radiopharmaceuticals) that are usuallyadministered intravenously to the patient. Whereas computed tomography(CT) and magnetic resonance imaging (MRI) provide information aboutanatomic structure, PET can image and quantify biochemical and/orphysiological function. This information is potentially valuable becausefunctional changes caused by disease are frequently detectable beforeany structural abnormalities become evident.

One embodiment of the present invention comprises a positron emissiontomography (PET) detector mounted onto the gantry arm 22 of the breastCT scanner 10 shown in FIG. 1, such that simultaneous acquisition of PETimages with the breast CT images can be accomplished. The PET image datawill provide information with regards to the functional status orphysiology of areas in the breast, including glucose metabolism andother functional or physiologic parameters. The CT scan will require ashorter period of time for acquisition, so the simultaneous imageacquisition refers to the dual modality imaging without repositioningthe patient. The positron emission tomography image data can be overlaidonto the anatomical images provided by the breast CT, thereby providingthe radiologist or other physician with an excellent map of thefunctional characteristics of breast tissues. In addition, the CT datamay be used to provide attenuation correction for the PET data.

7. Breast Restraint and Immobilization.

Referring now to FIGS. 26-30, a method and apparatus are disclosed forthe stabilization of compliant, or deformable, structures so that theymay be evaluated and manipulated in a controlled fashion. While thespecific application of the invention is the stabilization of breasttissue for applications, such as breast imaging, biopsy and otherprocedures, the broader applications of this invention extend to otherbiological tissues and areas beyond the medical arena.

In a preferred embodiment illustrated in FIG. 26, a breastimmobilization device 300 comprises a vacuum appliance 302, or suctioncup, made of a compliant material, such as silicone, and sized tocontact a small region of tissue of breast 40. The vacuum appliance 302is coupled to a vacuum source 306 via a tube 304. The vacuum source 306is configured to apply a contact vacuum on the interface surface 310 ofthe vacuum appliance 302, such that a slight tensile force may beapplied to the breast 40 to restrain the breast from motion. Afterplacement of the appliance 302 in contact with the skin surface, avacuum is applied to the appliance 302 that then immobilizes the skinsurface and extends to deeper tissues. For example, the appliance 302may be used to stabilize a region of the breast 40 with a suspiciouslesion at a depth below the surface.

Referring to FIG. 27, an interventional device 312 (e.g. biopsy needle,miniature surgical instrument, etc.) may be deployed through an accessport 308 in the vacuum appliance 302 and extended through superficialtissues to a target lesion 214 where the appropriate procedure isperformed. Through the multiplicity of orifices, a sufficiently largearea of tissue may be stabilized to permit high-resolution imaging orother procedures to occur without localized tissue motion.

Referring to FIGS. 28 through 30, the interface surface 310 may have aplurality of small orifices 314 in communication with the suction tube304, such that the suction may be applied evenly across the interfacesurface 310.

FIG. 29 illustrates a vacuum appliance 302 having a larger interfacesurface 310 for retention of the tissue. The orifices 314 may becircular, elliptical, rectangular etc., and typically will measure 0.1mm. to 5 mm. in diameter.

The geometry and construction of the vacuum appliance 302 are such thatit can be readily sterilized for surgical procedures. Further, thevacuum appliance 302 is of sufficiently simple design that productioncosts will be minimized, permitting mass production and disposableusage.

The immobilization device 300 may be used for retaining the breastduring scanning, minimally invasive device placement, or even forinvasive procedures. Breast immobilization would be highly beneficialfor high-resolution breast imaging, and for longer procedures, such asPETICT or radiation therapy. During physical biopsy, the immobilizationdevice 300 prevents the breast from recoiling under the force of anapplied needle puncture.

8. Radiation Therapy.

Once a breast tumor is located on the breast CT volume data set, theimaging system of FIG. 1 may be used in a high x-ray output mode toactually apply radiation therapy to the site of the lesion.

While high energy radiation beams produced at 2 MVp and higher are thetypical photon beams used in radiation therapy associated with both bodyand breast tumors, due to the smaller dimensions of the breast and thelow density composition of the breast (typically), it is possible toachieve highly concentrated radiation profiles in the breast using lowerenergy (kVp- or less than 1 MVp) radiation beams. Furthermore, theunique and nearly symmetrically cylindrical profile of the female breastwhen interrogated by a pendant geometry breast CT scanner, lends itselfideally to the use of relatively low energy x-ray spectra (e.g. heavilyfiltered 160 kVp, 320 kVp, up to 640 kVp).

In a preferred embodiment of the present invention, a method isdisclosed for using a breast CT scanner for energizing the x-ray systemat higher x-ray energies (e.g. 80 kVp or 100 kVp) for breast cancerdiagnosis or diagnostic examination and using a 160 or 320 kVp (etc.)x-ray beam for radiation therapy treatment. The advantages of a breastCT scanner in regards to the application of radiation therapy is theincreased spatial resolution accuracy that can be achieved on aper-fractionation basis with this modality. With each x-ray fraction, acomplete diagnostic breast CT scan (employing a cone beam, fan beam, ora hybrid fan beam/cone beam system) can be acquired with the patientlying stationary on the CT table. The treatment volume (typicallyconstituting both the tumor and an appropriate margin) is highlighted bythe radiation oncology professional after the breast CT volume datasetis reconstructed, using three-dimensional software and 3-dimensionalimage cursor technology commonly available to one skilled in the art.Once the treatment volume has been identified by the radiation oncologyprofessional, the breast CT scanner x-ray system can be energized athigher x-ray energies and at higher mA levels (e.g. 320 kVp and 20 mA)and a radiation therapy application can be applied to the identifiedtarget volume using rotational therapy techniques also available in theart.

In order for the x-ray beam to be collimated exclusively on the targetvolume as the x-ray source rotates 360 degrees around the breast hangingin pendant geometry, a CT radiation therapy system 320 with translatingcollimator system 322 (both in the x and z, or horizontal and verticaldirections) is shown in FIGS. 31 and 32. FIG. 31 shows the top-down viewof the breast CT scanner, including the x-ray source 24, x-raycollimator system 322, and detector 26 for breast CT acquisition. Thebreast 40 is illustrated as a circle in the center of the scan region(typically referred to as the isocenter). After the diagnostic breast CTacquisition, reconstruction, and interpretation, a cancer volume 214 canbe identified by the treatment physician as indicated by the blackcircle. This treatment volume may be exactly at the isocenter (notshown), or it could be at some distance away from the isocenter (asshown in FIGS. 31 and 32).

To enable the higher energy x-ray radiation therapy of this lesion awayfrom the isocenter, a preferred embodiment includes the translation of aradiation shield 324 in front of the x-ray detector 26 to protect itfrom the high radiation levels associated with radiation therapy, butalso to attenuate the radiation beam so as to record it and reconstructthe treatment volume, which can subsequently be overlaid onto thediagnostic breast CT volume dataset. Software for overlaying thereconstructed treatment volume with the diagnostic breast CT image mayalso be incorporated.

As the breast CT radiation therapy system 320 rotates around the breast,as depicted in FIG. 32, the collimator assembly 322 translatesaccordingly (in a sinusoidal fashion as described above for CT imagebiopsy and associated FIGS. 13-20) such that the high energy/highintensity x-ray beam 326 interrogates the designated treatment volume214.

FIG. 33 illustrates the collimator assembly 322 in a basic format totarget the radiation therapy. A left collimator assembly 340 has thecomponents as follows: a thick lead (or other highly attenuatingmaterial) x-ray shield 344, lead screws 346 or other translationalmechanical devices, a stationary mechanical framework 348, which housesa computer-controlled motor 350 (e.g., stepping or servo motor) thatrotates lead screws 346, resulting in the horizontal translation of thex-ray collimator shield 344. A mechanical end-piece 352 is provided toallow stabilization of the other end of the lead screws 346 near thecenter of the beam. The right collimator assembly 342 is essentially themirror image of the left collimator assembly 34 with working componentsas identified previously.

FIG. 34 illustrates a vertical collimator system 360 used for the breastCT radiation therapy system 320. This system allows the independentvertical translation of collimator blades using both a top assembly 362and a bottom assembly 364, as depicted. The vertical collimator system360 incorporates the same components as the horizontal collimator ofFIG. 33 (x-ray shield 344, lead screws 346, stationary mechanicalframework 348, motor 350, and mechanical end-piece 352) adjusted 90degrees.

The translating collimator assemblies 322, 362 are translatedhorizontally and vertically using a cable/pulley system (not shown) orother mechanical translation technology, which can be enabled undercomputer control, instead of the lead screws as shown in FIGS. 33-34.The drive mechanisms for these mechanical translation systems mayinclude stepping motors, linear motors, servo motors, and direct rotarymotor systems known in the art.

FIG. 35 illustrates the view from the x-ray source with both thehorizontal collimator system 322 and vertical collimator system 360 inthe field of view, resulting in a rectangular x-ray beam 366 profile.Multiple collimator assemblies, such as the 8-blade collimator system368 of FIG. 36, 16-blade collimator system 370, or even a 32-bladesystem (not shown) may be used to further define the x-ray beam profilebetter circumscribe circular lesions 214 identified within the breast40. Furthermore, collimator blades, which have circular, linear, orfinger-like projections relative to the treatment volume, may be used toenable more complicated and more exotic treatment volume profiles.

The benefits of the relatively low-energy radiation therapy treatmentsystem described herein, compared to MVp photon beams, include thehigher spatial resolution that the system affords, both by havingper-fraction target volume identification, and a smaller focal spot(which yields higher spatial resolution both for imaging and radiationtherapy treatment), and consequently a sharper profile x-ray beam due tothe lower energy (less oblique collimator penetration) and the smallerfocal spot (smaller penumbra) typical of kVp x-ray imaging systems.

Additional components of the CT radiation therapy system 320 describedabove include a software module to enable a per-fraction basis, modelsfor acquisition of a diagnostic breast CT exam data and the subsequentreconstruction of a volume dataset, a computer-aided or human-guided (orcombinations of above) identification of a 3-D tumor margin andtreatment volume module, and computer software necessary for driving themultiple collimator assemblies to deliver the targeted radiation therapybeam to the treatment volume.

A software module may also be included to modulate the kVp-x-ray energy,depending upon the position of the treatment volume relative to theisocenter and breast volume during the scan. For example, the kVp wouldbe increased when the amount of tissue that needs to be penetratedbetween the entrance beam and the tumor location increases, and areduction in kVp as the distance between the entrance site and the tumorvolume decreases. Software algorithms may further be used to determinethe optimum x-ray energy to optimize the radiation deposition of a tumorin a breast at a given thickness, which in turn enables the modulationof the kVp during rotational radiation therapy using the breast CTscanner and radiation therapy systems.

Other investigators have described the use of the injection of highatomic numbers (Z) materials, which preferentially leak into andconsequently surround the breast tumor in breast cancers to induce ashower of high linear energy transfer (LET) particles near the site ofthe tumor. Examples of these high Z agents include an iodinated contrastagent for CT or x-ray imaging, or gadolinium-based contrast agents forMR imaging. Other high Z agents are envisioned.

While these concepts have been previously disclosed by otherinvestigators, one embodiment of the current invention is a method ofscanning a region of interest with a radiation therapy breast CT alongwith the use of injected contrast agents to achieve increasedtherapeutic ratios for the treatment of breast cancer. An increasedtherapeutic ratio is achieved in this embodiment because the low energy(kVp) radiations are preferentially absorbed by the presence of thecontrast agent (using k-edge absorption techniques, well known- to thoseskilled in the art). Once the atoms associated with the contrast agentabsorb the radiation beam, subsequent radiations are emitted locally tothe site of those atoms, which are situated in close proximity to thebreast cancer tumor. The subsequent re-emission of lower energy x-raysand electrons has the effect of concentrating the therapeutic effect ofthe radiation at or near the site of the tumor for a more lethal effectthan the incident beam itself.

Examples of the secondary radiations include K, L, and M fluorescentradiations (x-ray photons), as well as Auger electrons and other cascadeelectrons associated with x-ray absorption. The net effect of thisembodiment is to selectively deliver higher radiation dose levels at thesite of the tumor, both by the selective nature of contrast agentsecretion near the site of the tumor, and the selective spatialirradiation achieved by the breast CT radiation therapy apparatus. Thus,combining radiation therapy at kVp x-ray energies with the injection ofcontrast injections may therefore lead to therapeutic ratios similar to,or better than, conventional radiotherapy techniques.

Referring now to FIG. 38, as an alternative to radiation therapy, highintensity focused ultrasound (HIFU) may be used for treating smalllesions in the breast, making use of the precise location of thecoordinates of a tumor determined as described above. In such a system,an HIFU application array 400 may be positioned against the skin of thebreast coupled with a suitable acoustic coupling material and as held bya robotically controlled arm 402 similar to any of the mechanical biopsyplacement systems described above. The application array 400 may beconstructed to provide a properly phased wavefront that passes into thebreast to converge on the site of the lesion to provide ablating energyto kill any cancer cells at a focal point. The phasing may be providedby well known phased-array techniques or by proper shaping of the array40. The array 400 may work in conjunction with the immobilization devicedescribed above or a separate immobilization arm 404 may be used. Again,real time imaging can be used to ensure proper registration of the focalpoint of the array 400 and the lesion.

9. Breast CT dosimetry.

One embodiment of the present invention comprises a method for measuringthe standard dose that is achieved during conventional two-viewmammography. The techniques used for producing the breast CT imagesdisclosed in Boone et al., Dedicated Breast CT: Radiation Dose and ImageQuality Evaluation, previously incorporated by reference, may be used todetermine the dosage for two-view mammography. These results may then beused to tailor the radiation dose from breast CT to be substantiallysimilar or identical to that of two-view mammography.

10. Dual Energy Projection Mammography.

The breast CT scanner consists of an x-ray tube, opposed to an x-raydetector, mounted on a rotating gantry system. If iodine, gadolinium, orsome other contrast agent is injected into the breast, dual energyimages can be acquired using this same x-ray detector system withoutrotating the gantry. Instead of acquiring tomographic data, thisprocedure would allow the acquisition of projection image data sets. Byusing one low-energy acquisition, and one high-energy acquisition, withsuitable processing, a dual energy subtraction image can be producedwhich highlights the tumor and makes it more visible from the backgroundbreast tissues. Monitoring the time-change in tumor contrast (followingthe wash-in and wash-out kinetics) is also disclosed as a possiblediagnostic tool.

11. Calibration Phantoms

In a breast CT, it is important for reconstruction algorithms used toreconstruct the acquired image data to make use of the geometry in whichthe images were acquired. To enable this, a method of the presentinvention uses a phantom consisting of a series of BBs placed in thefield of view to be imaged by the breast CT scanner. The individual BBsare then tracked using a tracking algorithm, and then the paths of eachBB are used to computer-fit the geometry of the scanner. This techniqueis a highly beneficial component of producing high-resolution CT imageswithout artifacts.

In addition to geometrical phantoms, phantoms comprised of variousbreast-like materials may be used to enable the accurate calibration ofthe CT image numbers (typically called Hounsefield units, HU). Accuratecomputation of the HUs in the breast CT will enable betterdifferentiation between adipose tissues, glandular tissues,microcalcifications, and breast cancer.

12. Three-Dimensional Breast CT Display.

As described above with respect to FIG. 6, one embodiment of the presentinvention comprises display techniques for optimally demonstrating thethree-dimensional anatomy of the breast for diagnosis. Specifically, athree-orthogonal view display package is disclosed, which enables theevaluation of the breast CT data from any arbitrary reference point. Anembodiment comprises simultaneous display of the axial, coronal, andsagittal images of the breast. In addition, other custom rotationscontrollable from input from a computer mouse may be achieved.Furthermore, alignment lines may be used on the computer monitor toallow a specific location within the breast to be identifiedsimultaneously on all three (or more) images of the breast. The displaysoftware for rendering the CT volume data set may also include thegeneration of mammogram-like images, so that the radiologist can comparethe tomographic images with an image that is more similar to theirtraining. The computer-generated mammographic images can also beaccompanied by the actual digital mammographic images for that woman.

13. Computer-Aided Detection. Computer-Aided Diagnosis.

The breast CT volume data sets generally have a much better signal tonoise ratio than screen film or digital mammographic images.Consequently, the application of computer algorithms to assist theradiologist or other physician in locating breast cancer (when present)is disclosed. Computer-aided diagnosis applied to breast CT data setswill likely perform better than those previously described for theevaluation of breast cancer on mammograms, due to the significantlyhigher signal to noise ratio of the breast CT data set. Algorithms forcomputer-aided detection involve assisting the radiologist (or otherphysician) in identifying areas in the volume data set which aresuspicious and may be breast cancer.

A second class of algorithms, called computer-aided diagnosis, may bethen used to perform evaluations on the specific characteristics of theshape, texture, and dimension (etc.) of the suspected area to develop aprobability of abnormality or a malignancy.

14. Automatic Tracking of Normal Ductal Structures.

The breast tissues of each individual woman are unique for that woman,but ductal patterns obey similar architectural laws based uponobservations of breast CT images. The ducts generally lead from thenipple then track posteriorly through the breast in linear or “warpedsheet” patterns. In one embodiment, an algorithm is used to identify thenormal ductal structure of a number of patients to build a database ofstructures that help to identify normal structures within the breast tohelp the diagnostician (radiologist or other physician) to rule out orbetter distinguish areas of suspicion.

15. Other Therapeutic Applications.

The volume data set provided by the breast CT has a high degree ofspatial accuracy, and this means that other radiation and nonradiationcan be applied to the breast under image guidance. Examples include thehigh-energy radiation beams described previously, as well as opticalradiation, high-intensity focused ultrasound (HIFU) beams, and radiofrequency waves which are capable of ablating the breast cancer. Thebenefit of these therapeutic approaches is that surgery may not berequired, and the tumor itself may be completely killed under theapplication of such therapies.

Although the description above contains many details, these should notbe construed as limiting the scope of the invention, but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. For example, the above disclosure is directed to usein imaging the breast of the patient. However, the methods and apparatusof the present invention may be used for imaging any area of anatomy ona patient. In many cases, the volume data need not be collected by x-raycomputed tomography and other forms of volume data acquisition may alsobe used with embodiments of the present invention. Therefore, it will beappreciated that the scope of the present invention fully encompassesother embodiments which may become obvious to those skilled in the art,and that the scope of the present invention is accordingly to be limitedby nothing other than the appended claims, in which reference to anelement in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structural,chemical, and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to thepublic, regardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. 112, sixth paragraph, unlessthe element is expressly recited using the phrase “means for.”

What is claimed is:
 1. A system for performing a simulated computedtomography (CT) breast biopsy, comprising: an x-ray source coupled to agantry that rotates around a subject's breast; a first detector and asecond detector both coupled to said gantry and positioned to receivex-ray beams from the x-ray source; and a processor communicativelycoupled to said first and second detectors and configured to: generate,based on a first x-ray beam received by the first detector, a first CTprojection dataset of the subject's breast at a first spatialresolution; identify, based on the first CT projection dataset, alocation of a possible tumor in the subject's breast; generate, based ona second x-ray beam received by the second detector, a second CTprojection dataset of a portion of the subject's breast proximate to thepossible tumor at a second, higher spatial resolution; and generate,based on at least the second CT projection dataset, a high-resolutionimage of the portion of the subject's breast.
 2. The system of claim 1,wherein the processor is further configured to generate thehigh-resolution image of the portion of the subject's breast based on acombination of the first CT projection dataset with the second CTprojection dataset.
 3. The system of claim 1, wherein the first detectorhas a first area and a first spatial resolution, and wherein the seconddetector has a second area smaller than the first area and a secondspatial resolution greater than the first spatial resolution.
 4. Thesystem of claim 1 further comprising a collimator assembly coupled tothe gantry and positioned between the x-ray source and the subject'sbreast, said collimator assembly configured to restrict the second x-raybeam to the portion of the subject's breast.
 5. The system of claim 4further comprising a collimator positioning system that is configured tomove the collimator assembly such that the second x-ray beam remainscentered on the portion of the subject's breast during motion of thegantry.
 6. The system of claim 1, wherein the x-ray source comprises anx-ray focal spot, the system further comprising an x-ray sourcepositioning system that is configured to move the x-ray focal spot suchthat the second x-ray beam remains centered on the portion of thesubject's breast during motion of the gantry.
 7. The system of claim 1further comprising a detector positioning system that is configured tomove the second detector during motion of the gantry such that thesecond detector receives the second x-ray beam during motion of thegantry.
 8. A method for performing a simulated computed tomography (CT)breast biopsy, comprising: generating, based on a first x-ray beamreceived by a first detector, a first CT projection dataset of asubject's breast at a first spatial resolution; identifying, based onthe first CT projection dataset, a location of a possible tumor in thesubject's breast; generating, based on a second x-ray beam received by asecond detector, a second CT projection dataset of a portion of thesubject's breast proximate to the possible tumor at a second, higherspatial resolution, wherein the first x-ray beam and the second x-raybeam are generated by an x-ray source; and generating, based on at leastthe second CT projection dataset, a high-resolution image of the portionof the subject's breast.
 9. The method of claim 8, wherein generatingthe high-resolution image of the portion of the subject's breastcomprises combining the first CT projection dataset with the second CTprojection dataset.
 10. The method of claim 8, wherein the firstdetector has a first area and a first spatial resolution, and whereinthe second detector has a second area smaller than the first area and asecond spatial resolution greater than the first spatial resolution. 11.The method of claim 8 further comprising: restricting the second x-raybeam to the portion of the subject's breast with a collimator assemblypositioned between the x-ray source and the subject's breast; and movingthe collimator assembly such that the second x-ray beam remains centeredon the portion of the subject's breast during motion of the x-ray sourceand the second detector.
 12. The method of claim 8 further comprisingmoving the second detector such that the second detector receives thesecond x-ray beam during motion of the x-ray source and the seconddetector.